The invention relates to a leak detection device with a high-vacuum pump implemented as a friction vacuum pump and two further vacuum pumps working against atmospheric pressure. The invention, furthermore, relates to a process for operating such leak detection device.
A leak detector of this type is disclosed in EU-A-283543. It operates according to the principle of counterflow (with helium as the test gas) and permits the detection of the impermeability of a test sample, respectively its permeability, and specifically gross impermeability to extremely small leaks (leakage rates up to 10.sup.-10 mbars l/s). In the helium leak detection with a device of the prior known type, the danger exists of hydrocarbon contamination occurring in the region of the test sample and/or the test chamber. These are caused by molecules which originate in the suction chambers of the oil-sealed vacuum pumps operating against atmospheric pressure and which diffuse back into the high-vacuum region against the delivery direction of the vacuum pump.